Field of the Invention
The present invention relates to a method for producing an L-amino acid utilizing a bacterium. L-amino acids are industrially useful as additives for animal feeds, ingredients of seasonings, ingredients of foods and drinks, amino acid infusions, and so forth.
Brief Description of the Related Art
L-Amino acids are industrially produced by, for example, fermentation using various microorganisms having an L-amino acid-producing ability. Examples of such methods for producing an L-amino acid by fermentation include, for example, methods of using a wild-type microorganism (wild-type strain), methods of using an auxotrophic strain derived from a wild-type strain, methods of using a metabolic regulation mutant strain derived from a wild-type strain as a mutant strain resistant to any of various drugs, and methods of using a strain having properties as both auxotrophic strain and metabolic regulation mutant strain.
In recent years, microorganisms in which an L-amino acid-producing ability is improved by recombinant DNA techniques are also utilized for production of L-amino acids. Examples of method for improving an L-amino acid-producing ability of a microorganism include, for example, enhancing the expression of a gene encoding an L-amino acid biosynthesis system enzyme (U.S. Pat. Nos. 5,168,056 and 5,776,736), and enhancing inflow of a carbon source into an L-amino acid biosynthesis system (U.S. Pat. No. 5,906,925).
In the conventional industrial production of objective substances such as L-amino acids by fermentation, glucose, fructose, sucrose, blackstrap molasses, starch hydrolysate, and so forth have been used as a carbon source.
It is also possible to use alcohols such as ethanol as a carbon source. As methods for producing an L-amino acid by fermentation using ethanol as a carbon source, there are known, for example, a method of using an Enterobacteriaceae bacterium modified so that it expresses alcohol dehydrogenase under aerobic conditions (WO2008/010565), a method of using an Enterobacteriaceae bacterium modified so that the activity of pyruvate synthase or pyruvate:NADP+ oxidoreductase is increased (WO2009/031565), a method of using an Enterobacteriaceae bacterium modified so that the activity of ribonuclease G is reduced (WO2010/101053), a method of using an Enterobacteriaceae bacterium modified so that it harbors a mutant ribosome S1 protein (WO2011/096554), a method of using an Enterobacteriaceae bacterium modified so that the activity of an A1 dB protein is reduced (WO2012/002486), and a method of using an Enterobacteriaceae bacterium modified so that the intracellular concentration of hydrogen peroxide is reduced (Japanese Patent Laid-open (Kokai) No. 2014-036576).
Aconitase is a dehydratase/hydratase that reversibly catalyzes the isomerization between citrate and isocitrate in the TCA cycle or glyoxylate cycle (EC 4.2.1.3). Escherichia coli has at least two kinds of isozymes of aconitase, AcnA and AcnB. The identity of the amino acid sequences of AcnA and AcnB is about 17%. AcnB is the major aconitase of Escherichia coli, and is expressed especially in the logarithmic phase (Cunningham L1, Gruer M J, Guest J R., Microbiology., 1997, December; 143(12):3795-805). On the other hand, AcnA is induced by iron or oxidization stress, and is expressed especially in the resting stage (Ho K K, Weiner H., J. Bacteriol., 2005, February; 187(3): 1067-73).
Acetaldehyde dehydrogenase is an enzyme that reversibly catalyzes the reaction of generating acetic acid from acetaldehyde by using NAD+ or NADP+ as an electron acceptor (EC 1.2.1.3, EC 1.2.1.4, EC 1.2.1.5, EC 1.2.1.22, etc.). For example, the AldB protein of Escherichia coli has the acetaldehyde dehydrogenase activity that uses NADP+ as an electron acceptor. As described above, it is known that a reduction of the activity of the AldB protein is effective for L-amino acid production using ethanol as a carbon source.